294 Journal of Agricultural Research voi. iv, no. 4 



Four varieties of phlox are employed in these experiments: Eclipse, 

 Large Yellow, Coccinea, and Camea. The Carnea variety was used as 

 the male parent in all of the crosses. 



Flowers that were practically colorless were recorded as "white" in 

 the tables, but, as the color plates show, a very slight amount of color 

 was present in many of them. They are probably not pure albinos. 



THE NATURE OF COLOR 



The colors of plants are due to constituents which are either colored 

 themselves or act upon other substances to produce color in them. All 

 of the cells of the plant contain these substances, with the possible excep- 

 tion of meristematic or rapidly growing tissue. Plant pigments may be 

 divided into two classes with reference to their location in the cell: 

 Chromoplast colors and cell-sap colors. The first class includes green, 

 usually yellow and orange, and occasionally red; the second class, mostly 

 red, blue, and violet. 



Buscalioni and Traverso distinguish the following classes: 



1. Green (chloroplasts). 



2. Yellow and orange (chromoplasts). 



3. White (colorless, made white by air in intercellular spaces). 



4. Red. 



5. Violet and lilac. 



6. Blue (4 to 6 anthocyan pigments in solution). 



7. Brown (tannin probably concerned). 



Various other colors are supposed to be due to the mixing or modifica- 

 tion of the pigments referred to. The black spots and stripes on the flow- 

 ers of the broad bean, for instance, are evidently due to violet pigment, 

 since the stripes at first are violet. 



The yellow color of flowers is due in most cases to chromoplasts con- 

 taining yellow anthoxanthin; but, rarely, yellow is a cell-sap color, as, 

 for example, in Mirahilis longiflora and the yellow parts of a white dahlia. 

 In the latter case there is a transition to red cell sap that establishes the 

 close relationship of these two colors. ♦ 



In yellow beets, also, there is yellow cell sap, probably closely related 

 to the red sap color of the beet. 



The yellow-brown colors found in seeds and fruits especially are con- 

 sidered to be largely due to tannin, which is itself colorless but readily 

 produces color through the action of carbon dioxid. 



Reds are usually cell-sap colors. Chrome reds and brick reds are excep- 

 tions. The tomato and the carrot, for instance, have red chromoplasts. 



The blue and the purple color substances in flowers are dissolved in the 

 cell sap and are distinguished for the most part from the plastid colors by 

 being insoluble in ether, xylol, benzol, chloroform, carbon disulphid, and 

 similar solvents, but are soluble in water or alcohol. 



